Tool holder of machine tool

ABSTRACT

A tool holder of a machine tool, wherein a holder rear end part is fixed to the front end part of the spindle of the machine tool, a tool receiving surface part  8   d  for receiving the rear end face of a shaft-like tool  11  fixed to a holder front end part so that a closed space in contact with the rear end face can be formed and mist cutting fluid passages  8   f   , 9   c  for leading mist cutting fluid fed from the front end part of the spindle to the closed space  12  are formed in a holder body at a center of rotation, and exhaust passages are formed for opening a part of the tool receiving surface part in contact with the closed space  12  to the atmosphere, whereby even when the shaft-like tool  11  is small in diameter and the amount of the mist cutting fluid flowing out to the atmosphere through a passage hole  11   a  in the shaft-like tool is small, the liquefied cutting fluid can be prevented from being accumulated in the mist cutting fluid passages by maintaining the flow velocity of the mist cutting fluid in the mist cutting fluid passages  8   f   , 9   c  at a proper level.

TECHNICAL FIELD

The present invention relates to a tool holder that has mist cuttingfluid fed from a spindle of a machine tool spout from the tip of ashaft-like tool.

PRIOR ART

In machining with a machine tool, much cutting fluid is fed to aworkpiece or a machining point to cool or lubricate a tool or to removecutting chips. In this case, there are many problems, such asenvironmental pollution, ill effects to human health, high cost causedby waste oil disposal of the cutting fluid, deterioration of the lifespan of the tool due to supercooling the workpiece , and sliding wear ofthe tool due to excessive cutting fluid in minute cutting. Besides,since much cutting fluid adheres to the cutting chips in machining, theadhered cutting fluid must be separated in the f disposal or recyclingof the cutting chips.

In recent years, to settle the above problems, there have appearedmachine tools performing so-called dry cutting that cut while feeding avery small quantity of mist cutting fluid to machining points.

A tool holder used in the machine tool is, for example, constructed asfollows. As shown in FIG. 11, a holder rear end part is fixed on a frontend of a spindle of the machine tool, and a tool receiving part 8 d andmist cutting fluid passages 9 c, 8 f are formed at a center of rotationR in a holder body 7. The tool receiving part 8 d receives the outsideperiphery of a rear end surface of a shaft-like tool 11 fixed on aholder front end part so as to form a closed space 12 in contact withthe rear end face. The mist cutting fluid passages 9 c, 8 f lead themist cutting fluid fed from the front end part of the spindle to theclosed space 12.

During machining with the shaft-like tool 11, the mist cutting fluid fedfrom the spindle reaches the closed space 12 through the passages 9 c, 8f, thereafter flowing from the front face of the shaft-like tool 11through passage holes 11 a, 11 a formed in the thickness portion thereof

In the above-mentioned dry cutting, for example, although the shaft-liketool 11 having a small diameter of about 1 mm to 5 mm is used, thediameter of the passage holes 11 a is about 0.1 mm to 0.5 mm, which isremarkably smaller than that of the passages 9 c, 8 f.

The small diameter of the passage holes 11 a diminishes the amount ofoutflow of the cutting fluid therethrough per hour, therebydeteriorating the flow velocity of the mist cutting fluid in thepassages 9 c, 8 f.

In this situation, when the tool holder rotates over about 6000 timesper minute, mist cutting fluid to be fed into the passages 9 c, 8 f orthe closed space 12, which is likely to stagnate, is affected bycentrifugal force due to the rotation, thereby promoting liquefying.Since liquefied cutting fluid can not flow as easily as mist cuttingfluid, it is gradually accumulated in circularity on wall faces of thepassages 9 c, 8 f and comes to restrict the flow of the mist cuttingfluid with progress of time. And finally, it becomes difficult to feed asufficient quantity of mist cutting fluid to the tip of the shaft-liketool 11.

The present invention aims to solve the above-mentioned problems and toprovide a tool holder of a machine tool having a required quantity ofmist cutting fluid continuously flowing from the tip of a shaft-liketool.

SUMMARY OF THE INVENTION

To achieve the above-mentioned aim, a first feature of the presentinvention is constructed as follows. That is, a tool holder is soconstructed that a tool receiving surface part for receiving a rear endface of a shaft-like tool fixed on a holder front end part so that aclosed space in contact with the rear end face can be formed, mistcutting fluid passages for leading mist cutting fluid fed from a frontend part of a spindle to the closed space are formed at a center ofrotation of a holder body, and exhaust passages are formed for openingthe closed space 12 (especially, a part of the tool receiving surfacepart) to the atmosphere except for the passage holes 11 a of theshaft-like tool 11 in contact therewith.

According to this, even if only a little mist cutting fluid passesthrough the passage holes of the tool because the shaft-like tool issmall in diameter, the mist cutting fluid in the closed space flows fromthe exhaust passages to the atmosphere with a suitable flux and the mistcutting fluid passages are decompressed. Therefore, the mist cuttingfluid in the mist cutting fluid passages has the flow velocitymaintained at proper levels, so as to be restricted from liquefying.Besides, even if the mist cutting fluid is liquefied, it is immediatelycarried into the closed space by the mist cutting fluid with a largeflow velocity, thereafter flowing to the atmosphere through the passageholes of the shaft-like tool and the exhaust passages.

In this case, it is preferable that the exhaust passages have a circularportion of outer concentric portion of mist cutting fluid passages nearthe rotating center of the closed space open to the atmosphere.According to this, the tool holder can improve in the symmetry to therotating center and maintain rotating stability in high-speed rotation.Besides, an effect of centrifugal force is that dense mist cutting fluidor droplets are actively led into the passage hole 11 a along an insidewall of the closed space to lubricate the tip of the tool.

According to a second feature of the invention, a holder rear end partis fixed on a front-end part of a spindle of a machine tool. Andbesides, a tool holder is so constructed that a tool receiving surfacepart receives a rear end face of a shaft-like tool fixed on a holderfront end part so that a closed space in contact with the rear end facecan be formed, and mist cutting fluid passages for leading mist cuttingfluid fed from a front end part of a spindle to the closed space areformed at a center of rotation of a holder body. Here, the toolreceiving surface part is excavated rearward to form an excavated partcomparatively large in diameter. On the other hand, the front end partsof the mist cutting fluid passages protrude so as to form a circularspace between its peripheral part and the excavated part. Besides,exhaust passages are formed for opening a circular portion of outerconcentric portion of the mist cutting fluid passages near the center ofrotation of the rear end face of the excavated part to the atmosphere.In this case, it is preferable that a diameter of the excavated part 8 gis about equal to the distance between the passage holes 11 a in aradial direction.

According to this, in addition to the same effects as the first feature, the following effects can be gained. Since the mist cutting fluid inthe front-end part of the mist cutting fluid passages flows into theclosed space near the rear end face of the shaft-like tool, it is notmuch affected by the excavated part, which is comparatively large indiameter. Therefore, the mist cutting fluid is prevented from liquefyingin the closed space, instead effectively flowing to the atmospherethrough the passage holes of the shaft-like tool. Besides, even if theliquefaction is temporarily excessive in the mist cutting fluidpassages, the liquefied cutting fluid is temporarily accumulated in theexcavated part. According to this, the liquefied cutting fluid can notinterrupt the outflow of the mist cutting fluid through the passageholes of the shaft-like tool. In this case, the front end part of themist cutting fluid passages can effectively restrict mixing and stirringthe cutting fluid temporarily, much accumulated along the insideperiphery of the excavated part with the mist cutting fluid flowingtherefrom. Moreover, when the diameter of the excavated part is aboutequal to the distance between the passage holes 11 a, 11 a, the densemist cutting fluid or the droplets near the wall of the excavated. partare immediately and actively led to the passage holes 11 a, 11 a by theeffect of centrifugal force .

The above-mentioned features can be embodied as follows.

The tool receiving surface part forms a front-end face of atool-receiving member adjustable in a longitudinal position in theholder body. According to this, even if the longitudinal position of theshaft-like tool is changed by longitudinally displacing thetool-receiving member, the effects of the above-mentioned inventions canbe gained. Here, since the tool-receiving member in the presentinvention is the same as that used in a conventional tool holder,different members for forming it are not especially needed.

In addition, a tool receiving member portion of the rear of theexcavated part forms a double pipe structure concentric with the centerof rotation thereof. The inside of an inner tube of the double pipestructure part forms a part of the mist cutting fluid passages, and acircular space between the inner tube and an outer tube thereof formsthe first exhaust passage portion by opening into the excavated part. Inthis case, the circular space preferably reduces the diameter of thefirst exhaust passage 8 k to the excavated part. According to this, theexhaust passage becomes superior in symmetry with respect to the centerof rotation of the tool holder, thereby securing the rotationalstability thereof in high speed rotation, as well as preventing densemist cutting fluid or the droplets from flowing therein.

Furthermore, the rearward circular space is so formed as to open to theatmosphere through an inner space of a holder body portion surroundingthe rear end part of the double pipe structure part, the second exhaustpassage portion, and a space of a tool fixing part formed to the frontend part of the holder body. Here, the second exhaust passage is formedbetween the tool receiving member and the holder body. Accordingly, theoutside periphery of the tool is efficiently lubricated.

Besides, an automatic switching valve is provided in the exhaustpassage, which opens when air pressure in the closed space is more thana fixed level. According to this, the automatic switching valve opensonly when the mist cutting fluid is apt to stagnate in the mist cuttingfluid passages, and the mist cutting fluid flows from the exhaustpassages to the atmosphere, thereby decompressing the mist cutting fluidpassages. Therefore, the mist cutting fluid therein improves in flow.

Moreover, a cylindrical valve for switching the exhaust passage and aspring for pressing the cylindrical valve forward are externallyinserted and mounted on the periphery of the mist cutting fluid passagesat the rearward tool receiving member portion of the double pipestructure part. When the air pressure of the closed space is more thanthe fixed level, the cylindrical valve is pressed and displaced rearwardagainst an elastic force of the spring to open the exhaust passage.Conversely, when it is less than the fixed level, the cylindrical valveis pressed and displaced forward by the elastic force to close it.According to this, the cylindrical valve and the spring become superiorin symmetry with respect to the center of rotation of the tool holder,thereby improving the rotational stability thereof as well as making theautomatic switching valve compact.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view from the side of a spindle device of amachine tool having a tool holder showing an embodiment of the presentinvention.

FIG. 2 is a sectional side view of the tool holder.

FIG. 3 is an enlarged sectional view around a tool receiving member ofthe tool holder.

FIG. 4 is a sectional view taken on line x-x in FIG. 1.

FIG. 5 is a sectional view taken on x1-x1 in FIG. 1.

FIG. 6 is a sectional view taken on x2-x2 in FIG. 1.

FIG. 7 is an explanatory view showing a proper flow situation of cuttingfluid in the tool holder.

FIG. 8 is an explanatory view showing an operational condition of afirst variation of the embodiment of FIG. 1.

FIG. 9 is an explanatory view showing another operational condition ofthe first variation.

FIG. 10 is a sectional side view showing a second variation.

FIG. 11 is a sectional side view of a conventional tool holder.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The present invention will be explained as follows with reference to thedrawings.

FIG. 1 is a sectional side view of a spindle device of a machine toolhaving a tool holder showing an embodiment of the present invention, andFIG. 2 is a sectional side view of the tool holder. FIG. 3 is anenlarged sectional view around a tool receiving member of the toolholder. FIG. 4 is a sectional view taken on line x-x in FIG. 1, FIG. 5is a sectional view taken on x1-x1 in FIG. 1, and FIG. 6 is a sectionalview taken on X2-x2 in FIG. 1.

In these figures, 1 is a spindle of a machine tool, which has a taperhole 1 a and coaxial large and small holes 1 b, 1 c at a center ofrotation R thereof. A cylindrical clamp part 2 comprising alarge-diameter part 2 a and a small-diameter part 2 b and a draw barpart 3 for longitudinally displacing the cylindrical clamp part 2 areinserted in the centers of the holes 1 a, 1 b, 1 c. In addition, aplurality of spindle-side collets 4 is circularly engaged between thecylindrical clamp part 2 and the spindle 1.

In this case, a straight mist cutting fluid passage 5 is formed at thecenters of the cylindrical clamp part 2 and the draw bar part 3,transferring mist cutting fluid generated outside or inside the spindle1 to a front f1 of the spindle 1.

The cylindrical clamp part 2 moves in a longitudinal direction f withthe draw bar 3. The draw bar is comparatively small in diameter. In thiscase, when the draw bar 3 is displaced in the front direction f1, thelarge-diameter part 2 a goes through the spindle-side collets 4 group inthe front direction f1, and the rear end part of the small-diameter part2 b moves forward of the rear end of each spindle-side collet 4 on theperiphery thereof Accordingly, the circular spindle-side collets 4 groupis freely displaced in a radial direction. Conversely, when the draw bar3 is displaced in a rear direction f2, the large-diameter part 2 a ismoved from outside of the spindle-side collets 4 group in the reardirection f2 to interfit with the group of spindle-side collets, and therear end part of the small-diameter part 2 b is moved into the rear endof each spindle-side collet 4 to interfit therewith. Accordingly, thediameter of the spindle-side collets 4 group is enlarged to the maximumto be fixed in place.

Numeral 6 is a tool holder 6 of the present invention, fixed on thespindle 1 concentrically with the center of rotation R thereof The toolholder 6 is provided with a holder body 7, a tool receiving member 8, aprotuberant connecting member 9 and a tool fixing part 10.

The holder body 7 is symmetric with the center of rotation R, comprisinga gripped part 7 a, a cylindrical tapered shaft part 7 b, a straightpart 7 c, an external thread part 7 d, a circular concavity 7 e, aradial surface part 7 f, an internal thread 7 g, a tapered hole 7 h, athread hole 7 i and a small-diameter hole 7 j, as shown in FIG. 2. Thegripped part 7 a is large in diameter. The cylindrical tapered shaftpart 7 b is provided to the rear f2 of the gripped part 7 a, and thestraight part 7 c is provided to the front fl thereof. The externalthread part 7 d is formed to the front of the straight part 7 c. Thecircular concavity 7 e is formed on the inside periphery of the taperedshaft part 7 b, and the radial surface part 7 f is formed on theforefront end thereof The internal thread 7 g is formed at the center ofthe radial surface part 7 f The tapered hole 7 h is formed at the frontf1 of the inside of the straight part 7 c, and the thread hole 7 i isformed to the rear f2 thereof so as to communicate with the tapered hole7 h. Besides, the small-diameter hole 7 j is formed at the center of thegripped part 7 a for communicating the internal thread 7 g with thethread hole 7 i.

The tool receiving member 8, which is screwed into the thread hole 7 idisplaceably in the longitudinal direction f, comprises an externalthread part 8 a and a slender passage part 8 c. The slender passage part8 c extends from the rear end face 8 b of the external thread part 8 ain the rear direction f2 to be inserted into the small-diameter hole 7j. The front end face of the external thread part 8 a forms a taperedtool receiving surface part 8 d for receiving the outside periphery ofthe rear end face of a shaft-like tool 11 such as a drill so as to forma closed space 12 contacting the rear end face. In addition, a secondexhaust passage 8 e is provided between the external thread part 8 a andthe thread hole 7 i by forming a longitudinal grooved passage on aperipheral thread surface of the external thread part 8 a Moreover, astraight mist cutting fluid passage 8 f comparatively small in diameteris formed att the center of rotation R of the external thread part 8 aand the slender passage part 8 c.

A circular hole-like excavated part 8 g is formed at the center of thetool receiving surface part 8 d of the external thread part 8 a,extending in the rear direction f2, the excavated part having a largerdiameter than the forward mist cutting fluid passage 8 f. The front endpart 8 h of the forward mist cutting fluid passage 8 f protrudes fromthe rear end face of the excavated part 8 g in the front direction f1,and a forward opening thereof is located as close as possible to therear end face of the shaft-like tool 11.

The rear of the excavated part 8 g of a part of the external thread part8 a forms a double pipe structure part as shown in FIG. 3. The inside ofan inner pipe part 8 i forms a part of the forward mist cutting fluidpassage 8 f. A circular space 8 k between an outer pipe part 8 j and theinner pipe part 8 i forms the first exhaust passage portion, having afront end opening in the excavated part 8 g and a rear endcommunicating. with radial holes 8 m, 8 m formed in the thickness of thefront end face of the slender passage part 8 c. In this case, the frontend of the first exhaust passage portion 8 k is located near the centerof rotation of the rear end face of the excavated part 8 g, making acircular portion concentric with the center of rotation R and opening‘a’.

The protuberant communicating member 9, as shown in FIG. 2, comprises acomparatively short external thread part 9 a and a straight protrudingpart 9 b. The external thread part 9 a is screwed to the internal threadpart 7 g in order to be integrally fixed on the holder body 7. Thestraight protruding part 9 b is so constructed that a straight rearwardmist cutting fluid passage 9 c for extending the forward mist cuttingfluid passage 8 f in the rear direction f2 is provided at the center ofrotation R, and that the periphery of the rear end part is inserted intothe forward-enlarged part 5 a of the mist cutting fluid feeding passage5. In this case, the slender passage part 8 c is inserted into the frontof the rearward mist cutting fluid passage 9 c, and the forward mistcutting fluid passage 8 f and the rearward mist cutting fluid passage 9c in the slender passage part 8 c are airtightly communicated through asealing member. Besides, the straight protruding part 9 b and theforward-enlarged part 5 a are airtightly communicated through a sealingmember fixed thereon.

The tool fixing part 10 comprises three tool collets 13 and a fasteningnut body 14. The tool collets 13 are circularly interfitted into thetapered hole 7 h. The fastening nut body 14 is externally screwed on theexternal thread part 7 d to displace the circular tool side collets 13group in the longitudinal direction f. In this case, when the fasteningnut body 14 is turned in a closing direction around the center ofrotation R, it presses the tool side collets 13 group in the reardirection f2 to reduce the diameter due to interaction with the taperedhole 7 h. Conversely, when it is turned in the opposite direction, itpulls the tool side collets 13 group in the front direction f1 to expandthe diameter.

The base part of the shaft-like tool 11 is inserted into the centralhole of the tool side collets 13 group. In this case, by turning thefastening nut body 14 in the above-mentioned closing direction, the basepart of the shaft-like tool 11 is fastened to the tool side collets 13group in order to be integrally fixed on the holder body 7 by beingdrawn in the rear direction f2. Besides, the periphery of the rear endface of the shaft-like tool 11 is airtightly pressed on the toolreceiving surface part 8 d. Conversely, according to rotating it in theopposite direction, the tool side collets 13 group is displaced so as toexpand the diameter to enable the base of the shaft-like tool 11 to bepulled out of the central hole.

The shaft-like tool 11 is provided with passage holes 11 a, 11 a forpassing cutting fluid in a longitudinal direction through one or aplurality of portions (in figures, two portions) of the thickness . Acutting part of the shaft-like tool like can have various sizes indiameter, occasionally 1 mm to 5 mm. The diameter of the passage hole 11a of a cutting part having a small diameter like this is, for example,about 0.1 mm to 0.5 mm. These passage holes 11 a, 11 a have inletopenings and outlet openings on the rear end face and on the front endface of the shaft-like tool 11, respectively. In this case, two inletopenings are located in the closed space 12.

In the above-mentioned structure, the forward mist cutting fluid passage8 f and the rearward cutting fluid passage 9 c serve as a mist cuttingfluid passage of the tool holder 6. Besides, the first exhaust passageportion 8 k, two radial holes 8 m, 8 m, an internal space 15 of theholder body 7 surrounding the peripheral rear part of the double pipestructure part of the external thread part 8 a, the second exhaustpassage portion 8 e, an internal space 16 of the holder body 7surrounding the front of the external thread part 8 a, and a spacebetween the tool side collets 13, etc. serve as an exhaust passage foropening a part of the tool receiving surface part 8 d abutted on theclosed space 12 to the atmosphere.

An explanation about the operation of each part, using an example of theabove-mentioned device, is as follows.

When fixing the tool holder 6 on the spindle 1, at first, the draw barpart 3 is displaced in the rear direction f2 to displace the cylindricalclamp part 2 thereto, and therefore, the spindle side collets 4 group incircular arrangement is freely displaced to reduce diameter.

In this situation, the tapered shaft part 7 b of the tool holder 6 ispushed into the tapered hole 1 a of the spindle 1 with the gripped part7 a gripped. Hence, the tapered shaft part 7 b is deeply inserted intothe tapered hole 1 a by reducing the diameter of the spindle sidecollets 4 group at the inside periphery thereof The forefront largediameter part 4 a of the spindle side collets 4 group is located in thecircular concave part 7 e of the inside periphery of the tapered shaftpart 7 b. Besides, the rear end part of the protuberant communicatingmember 9 is interfitted into the forefront enlarged part 5 a toairtightly communicate the mist cutting fluid feeding passage 5 with therearward mist cutting fluid passage 9 c.

Thereafter, the draw bar 3 is pulled in the rear direction f2 to enlargethe diameter of the spindle side collets 4 group. Here, the forefrontlarge diameter part 4 a is engaged with the circular convex part 7 e.Then, the tapered shaft part 7 b is pulled to the rear direction f2 tobe exactly-concentrically fixed on the specified position of the spindle1 as shown in FIG. 1.

Besides, when the fixed tool holder 6 is detached from the spindle 1,the steps for fixedly attaching it thereon are performed in reverseorder.

When machining a work, first of all, the spindle 1 is rotated, and themist cutting fluid is fed into the mist cutting fluid feeding passage 5of the spindle 1 from the rear thereof. In this case, the rotation ofthe spindle 1 is transmitted to the tool holder 6 by friction forcecaused between the tapered hole 1 a and the tapered shaft part 7 b torotate the tool holder 6 concentrically therewith. Here, the mistcutting fluid may be generated outside the spindle 1 or thereinside. Themist cutting fluid inside the mist cutting fluid feeding passage 5reaches the forward mist cutting fluid passage 8 f through the rearwardcutting fluid passage 9 c, and then, the inside of the closed space 12covering the rear end face of the shaft-like tool 11, continuously.Thereafter, it spouts from the outlet opening of the front end face ofthe shaft-like tool 11 through the passage holes 11 a, 11 a, andbesides, flows to the atmosphere in front of the tool fixing part 10through the exhaust passage comprising the first exhaust passage portion8 k, the internal space 15 of the thread hole part 7 i on the rear ofthe external thread part 8 a, the second exhaust passage part 8 e, andeach space among three tool side collets 13 of the tool fixing part 10.

Next, the spindle 1 is displaced toward the workpiece to cut it on thefront end of the shaft-like tool 11. During this cutting process, themist cutting fluid flowing out of the front end of the shaft-like tool11 lubricates the portion of the workpiece being cut.

During such machining , when the spindle 1 rotates more than 6000 timesper minute and the passage hole 11 a is small, as in a small-diametertool, the mist cutting fluid in a passage group comprising the mistcutting fluid feeding passage 5, the rearward mist cutting fluid passage9 c, the forward mist cutting fluid passage 8 f and the closed space 12receive strong centrifugal force due to the rotation of the tool holder6, and liquefaction is promoted. In this case, when the mist cuttingfluid does not flow out of the exhaust passages to the atmosphere, theflow velocity thereof in the passage group is excessively slow becauseof the small flow quantity flowing out of the passage holes 11 a, 11 aTherefore, the liquefaction of the mist cutting fluid is greatlypromoted. The liquefied cutting fluid stagnates in the passage group soas to gradually accumulate, and consequently, a comparatively long timeis needed for reaching the tip of the tool.

However, in fact, since the mist cutting fluid reaching the closed space12 flows out of the exhaust passages to the atmosphere in an adequateflow quantity, the flow velocity thereof in the passage group isincreased, and consequently, a self-stirring function is increased.Therefore, the liquefaction of the mist cutting fluid can be restricted.Besides, even. if the mist cutting fluid is partially liquefied, theliquefied cutting fluid can make the mist cutting fluid flow into theclosed space 12 rapidly in a large flow velocity. In this case, the highdensity and low density mist cutting fluids smoothly flow into thepassage hole 11 a and into the exhaust passages, respectively.Therefore, even if machining time is prolonged , an excess of liquefiedcutting fluid is not accumulated on the inner wall surfaces of the mistcutting fluid passages 9 c, 8 f in circularity, as happened previously .Accordingly, the flow quantity of mist cutting fluid flowing out throughthe passage holes 11 a, 11 a during the work machining is enough tolubricate the work cutting portion of the shaft-like tool 11. FIG. 7shows a proper flow situation of the cutting fluid like this. As shownin this figure, the liquefied cutting fluid ‘b’ barely accumulates onlynear the inlet opening of the passage hole 11 a in circularity besidethe insides of the front end part 8 h and the closed space 12. Theaccumulated cutting fluid ‘b’ never grows, even if the time isprolonged.

In the above-mentioned flow of the mist cutting fluid, the forefront ofthe front end part 8 h is located near the rear end face of theshaft-like tool 11. Therefore, the mist cutting fluid flowing out thefront end part 8 h passes through the excavated part 8 g with a radiusof the same length as the distance from the center of the passage hole11 a, and the high density mist cutting fluid in it flows into thepassage holes 11 a, 11 a by centrifugal force.

During the machining operation, when excessive liquefaction temporarilyoccurs in the mist cutting fluid passages 5, 9 c, 8 f because either thetool holder 6 greatly increases in rotation velocity or the passageholes 11 a, 11 a are somewhat closed by cutting chips, etc., theliquefied cutting fluid is rapidly fed therefrom to the excavated part 8g by the mist cutting fluid at a large flow velocity. Then, it istemporarily accumulated therein, and thereafter flows to the atmospherethrough the passage 11 a. Accordingly, the mist cutting fluid in themist cutting fluid passages 5, 9 c, 8 f can flow stably.

Besides, since there exists an opening ‘a’ in the first exhaust passageportion 8 k on the circular portion around the center of rotation R ofthe rear end face of the excavated part 8 g, a gas component separatedfrom the mist cutting fluid by centrifugal force flows therefrom. On theother hand, a liquid component remains on the inside periphery of theexcavated part 8 g in circularity, and it flows out of the passage hole11 a when the remaining quantity increases.

Since the front end part 8 h protrudes from the rear end face of theexcavated part 8 g in the front direction f1, interference between theforward flow flowing out of the front end part 8 h and the rearward flowgoing for the first exhaust passage portion 8 k in the excavated part 8g is restricted. Therefore, the mist cutting fluid can flow effectivelyin the closed space 12.

A first variation of the above-mentioned embodiment will be explained asfollows. FIG. 8 is an explanatory view of working situation thereof, andFIG. 9 is an explanation view of another variation.

An automatically switching valve 17 is provided in the exhaust passage.The switching valve 17 comprises a cylindrical valve body 17 a, acoil-like spring 17 b and an engaging ring 17 c. The cylindrical valvebody 17 a covers the outlet openings ‘c’ of the radial holes 8 m, 8 m,being externally inserted on the outside periphery of the slenderpassage part 8 c airtightly and slidably in the longitudinal directionthrough a not-illustrated packing. Here, the outside periphery of theslender passage part 8 c serves as the peripheral wall part of theforward mist cutting fluid passage 8 f. The coil-like spring 17 b is topress the cylindrical valve body 17 a in the front direction f1, beingexternally inserted on the outside periphery of the slender passage part8 c and compressed by the engaging ring 17 c . In this case, the frontend face of the cylindrical valve body 17 a is formed so as toairtightly engage the rear end face 8 b of the external thread part 8 a

The varied embodiment is operated as follows. When the mist cuttingfluid in the closed space 12 flows to the atmosphere through the passageholes 11 a, 11 a in a quantity above a fixed flow quantity, the airpressure in the forward mist cutting fluid passage 8 f is comparativelylow. The flow velocity of the mist cutting fluid flowing in the passage8 f is made at a speed that does not excessively accumulate liquefiedcutting fluid in the mist cutting fluid passages 5, 9 c, 8 f. Therefore,the mist cutting fluid need not flow from the exhaust passages 8 k, 8 m,8 e. However, in this situation, as shown in FIG. 8, the front end faceof the cylindrical valve body 17 a is displaced in the front directionf1 by the spring 17 b, airtightly engaging the rear end face 8 b of theexternal thread part 8 a Consequently, the cylindrical valve body 17 ablock the radial holes 8 m, 8 m. According to this, the mist cuttingfluid is prevented from flowing to the atmosphere needlessly.

On the other hand, when the mist cutting fluid in the closed space 12flows to the atmosphere through the passage holes 11 a, 11 a in aquantity below the fixed flow quantity, the pressure in the forward mistcutting fluid passage 8 f or the closed space 12 is comparatively high .The flow velocity of the mist cutting fluid flowing in the passage 8 fis decreased enough to excessively accumulate the liquefied cuttingfluid in the mist cutting fluid passages 5, 9 c, 8 f Therefore, the mistcutting fluid needs to flow out of the exhaust passages 8 k, 8 e.However, in this situation, as shown in FIG. 9, the cylindrical valvebody 17 a is displaced in the rear direction f2 against the spring 17 bby air pressure acting on the inside face thereof to be separated fromthe rear end face 8 b by a distance corresponding to the air pressure .Therefore, the radial holes 8 m, 8 m are communicated to the atmospherewith proper passage cross-section. According to this, the mist cuttingfluid adequately flows to the atmosphere, thereby preventing theliquefied cutting fluid from excessively accumulating in the mistcutting fluid passages 5, 9 c, 8 f.

Next, the second variation of the above-mentioned embodiment will beexplained. FIG. 10 is a sectional side view showing the variation. Asshown in this figure, the excavated part 8 g is not formed in the toolreceiving surface part 8 d, and the double pipe structure part is formednear the center of rotation of the external thread part 8 a similar tothe above example. That is, the inside of the inner tube part 8 i formsthe forward mist cutting fluid passage 8 f, and the circular spacebetween the inner tube part 8 i and the outer tube part 8 j forms thefirst exhaust passage 8 k. Accordingly, there are two differences fromthe above example, namely, special effects due to the excavated part 8 gand the front end part 8 h of the forward mist cutting fluid passage 8 fare not obtained, because the closed space 12 is narrow due to theabsence of the excavated part 8 g and the front end part 8 h does notprotrude in the front direction f1 in the closed space 12. However,there is an effect based on the outflow of a part of the mist cuttingfluid in the closed space 12 from the exhaust passages 8 k, 8 e to theatmosphere similar to the above example.

In this case, instead of the circular first exhaust passage 8 k, anon-circular longitudinal hole 8 k, such as a drill hole, may be formedin the thickness of the external thread part 8 a outside the forwardmist cutting fluid passage 8 f.

To simplify the structure, it can be so constructed that the mistcutting fluid in the closed space 12 is discharged through the radialholes of the holder body 7 and the external thread part 8 a Thisconstruction is also within the range of the present invention.

INDUSTRIAL APPLICABILITY

According to the present invention, the following effects will begained.

That is, even if the cutting fluid accumulates because the shaft-liketool 11 is small in diameter and little mist cutting fluid flows to theatmosphere through the passage hole 11 a and the flow in the passage ispoor, the cutting fluid is rapidly transferred by keeping the flowvelocity of the mist cutting fluid in the mist cutting fluid passages 5,9 c, 8 k at a proper level without changing the shaft-like tool 11. Arequired quantity of mist cutting fluid can continuously and stably flowfrom the front end of the passage hole 11 a.

Besides, the symmetry to the center of rotation can be easilymaintained, and the rotating stability is made superior even inhigh-speed rotation. The high density mist cutting fluid flows to thetip of the tool through the passage hole 11 a, and the low density mistcutting fluid goes around to flow to the atmosphere.

In addition to the above-mentioned effects, the following effects can begained. Even if the liquefaction in the mist cutting fluid passages 5, 9c, 8 k is temporarily too much, the liquefied cutting fluid istemporarily accumulated in the excavated part 8 g, which iscomparatively large in diameter, and the mist cutting fluid is stablyflowed through the mist cutting fluid passages 5, 9 c, 8 f and thepassage hole 11 a.Besides, the rotational influence of the excavatedpart 8 g to the mist cutting fluid flowed from the front end part 8 h ofthe mist cutting fluid passages 5, 9 c, 8 f is restricted, and the mistcutting fluid flowed into the closed space 12 can be prevented fromliquefying therein. Therefore, the mist cutting fluid in the closedspace 12 can effectively flow to the atmosphere through the passage hole11 a. Besides, the front end part 8 h of the mist cutting fluid passages5, 9 c, 8 f can restrict the mist cutting fluid flowing therefrom andmuch cutting fluid accumulated in the excavated part 12 in circularityalong the inside periphery thereof from being mixed and stirred.Accordingly, the mist cutting fluid in the closed space 12 caneffectively flow to the atmosphere through the passage hole 11 a.

Moreover, even if the longitudinal position of the shaft-like tool 11 ischanged, the above-mentioned effects can be gained, and besides, thecutting fluid can be actively led to the passage hole 11 a.

Furthermore, since the exhaust passages 8 k, 8 e are superior insymmetry with respect to the center of rotation of the tool holder, therotational stability of the tool holder at the time when it is rotatedin high speed is satisfactorily secured, and besides, the cutting fluidcan be actively led to the passage hole 11 a.

Besides, the mist cutting fluid can be applied on the tool withoutwaste.

Moreover, the mist cutting fluid in the closed space 12 can be flowedfrom the exhaust passages 8 k, 8 e to the atmosphere only when it isrequired, thereby preventing waste of the mist cutting fluid.

Furthermore, a structure for automatically flowing the mist cuttingfluid in the closed space 12 to the atmosphere through the exhaustpassages 8 k, 8 e only when it is required can be made compact withoutdamaging the rotational stability of the tool holder.

1. A tool holder of a machine tool, comprising: a holder body; a toolreceiving surface part for receiving a rear end face of a shaft-liketool so as to form a closed space in contact with the rear end face,said shaft-like tool being fixed on a front end of the holder body; andmist cutting fluid passages for leading mist cutting fluid fed from afront end part of a spindle to the closed space; wherein an exhaustpassage is formed for opening the closed space to the atmosphere, saidexhaust passage being in addition to a passage of the shaft-like tool incommunication with the closed space.
 2. A tool holder of a machine toolas claimed in claim 1, wherein said exhaust passage has a circularportion near a center of rotation of the closed spaces concentricallyoutside the mist cutting fluid passages open to the atmosphere.
 3. Atool holder of a machine tool, comprising: a holder body; a toolreceiving surface part for receiving a rear end face of a shaft-liketool so as to form a closed space in contact with the rear end face,said shaft-like tool being fixed on a front end of the holder body; andmist cutting fluid passages for leading mist cutting fluid fed from afront end part of a spindle to the closed space; wherein said toolreceiving surface part is excavated rearward to form an excavated partlarge in diameter, a front end part of said mist cutting fluid passagesprotrudes so as to form a circular space between a peripheral wall andthe excavated part, and wherein an exhaust passage is formed for openinga circular portion concentrically outside the mist cutting fluidpassages near a center of rotation of the rear end face of the excavatedpart to the atmosphere.
 4. A tool holder of a machine tool as claimed inclaim 1, wherein said tool receiving surface part forms a front end faceof a tool receiving member adjustable in longitudinal position in theholder body.
 5. A tool holder of a machine tool as claimed in claim 3,wherein said tool receiving surface part and said excavated part areformed on a front end face of a tool receiving member adjustable inlongitudinal position in the holder body, and a tool receiving memberpart at the rear of the excavated part forms a double pipe structureconcentric with its center of rotation, and wherein an inside of aninner tube of the double pipe structure forms a part of the mist cuttingfluid passages, and a circular space between the inner tube and an outertube of the double pipe structure opens into the excavated part to forma first portion of the exhaust passage.
 6. A tool holder of a machinetool as claimed in claim 5, wherein said exhaust passage portion opensto the atmosphere through a space formed at the front end part of theholder body and through an inner space of a holder body part surroundinga rear end part of the double pipe structure and a second portion of theexhaust passage formed between the tool receiving member and the holderbody.
 7. A tool holder of a machine tool as claimed in claim 1, whereinan automatic switching valve is provided in the exhaust passage, andsaid automatic switching valve opens when air pressure in the closedspace is above a fixed level.
 8. A tool holder of a machine tool asclaimed in claim 5, wherein a cylindrical valve for opening and shuttingthe exhaust passage and a spring for pressing said cylindrical valveforward are positioned on a peripheral wall part of the mist cuttingfluid passages on the tool receiving member portion of the rear of thedouble pipe structure, and wherein the cylindrical valve is pushed anddisplaced rearward against the elasticity of said spring due to the airpressure in the closed space to open said exhaust passage when the airpressure is above the fixed level, and conversely, the cylindrical valveis pushed and displaced forward due to the elasticity of said spring toclose said exhaust passage when said air pressure is below the fixedlevel.